Traditional heat exchangers include plate-fin heat exchangers and shell-and-tube heat exchangers. Previous efforts to improve upon traditional heat exchangers involve altering the heat exchanger architecture so as to increase the heat transfer while having minimal effect on pumping power. Straight fins gave rise to a number of variations including staggered fins, wavy fins, offset fins, and louvered fins. Twisted tape inserts have been placed inside tubes in shell and tube heat exchangers. Elliptical tubes have also been used. However, these architectures are constrained by the shapes that can be easily fabricated. For example, it is difficult and sometimes impossible to combine the advantages of multiple individual heat transfer enhancement design features utilizing existing methods.
Additive manufacturing (e.g. 3D printing) enables significantly more complex designs than traditional heat exchanger fabrication techniques and allows for individual heat transfer enhancement features that can be combined into a complex design.
Additive manufacturing has been used to print heat exchangers by directly printing the heat exchanger walls. This method has several limitations stemming from the minimum feature size that may be printed. Thin walls are preferable in heat exchangers to reduce the conductive thermal resistance across the walls and thus increase heat transfer. In addition, thin walls permit more of the heat exchanger volume to be occupied by the heat transfer fluids, which keeps the ratio of actual to superficial velocity low, and reduces (e.g., minimizes) the input pumping power required to operate the heat exchanger. Typically, walls of traditional heat exchangers may be as thin as 90 microns and more compact heat exchangers could be made if thinner walls could be reliably produced at large scales. Typical 3D-printed minimum feature sizes are 50-100 microns. Making a 3D-printed heat exchanger with one or only a few voxels through the thickness of the wall leads to a high surface roughness (e.g., due to aliasing) and leaky walls, both of which make for poor heat exchangers. Some 3D printers exist with feature sizes in one dimension as small as 16 microns, but as feature size is reduced, production time increases superlinearly.